Subject: Re: [PATCH net] net: phy: micrel: Fix MMD register access during SPD in ksz9131_resume()

From: Nicolai Buchwitz <[email-masked]>
Date: Fri, 03 Apr 2026 14:30:01 +0200

On 3.4.2026 13:17, Ovidiu Panait wrote:
> During system suspend, phy_suspend() puts the PHY into Software 
> Power-Down
> (SPD) by setting the BMCR_PDOWN bit in MII_BMCR. According to the 
> KSZ9131
> datasheet, MMD register access is restricted during SPD:
> 
>   - Only access to the standard registers (0 through 31) is supported.
>   - Access to MMD address spaces other than MMD address space 1 is
>     possible if the spd_clock_gate_override bit is set.
>   - Access to MMD address space 1 is not possible.
> 
> However, ksz9131_resume() calls ksz9131_config_rgmii_delay() before
> kszphy_resume() clears BMCR_PDOWN. This means MMD registers are 
> accessed
> while the PHY is still in SPD, contrary to the datasheet.
> 
> Additionally, on platforms where the PHY loses power during suspend
> (e.g. RZ/G3E), all settings from ksz9131_config_init(), not just the
> RGMII delays, are lost and need to be restored. When the MAC driver
> sets mac_managed_pm (e.g. stmmac), mdio_bus_phy_resume() is skipped,
> so phy_init_hw() (which calls config_init to restore all PHY settings)
> is never invoked during resume.
> 
> Fix this by replacing the RGMII delay restoration with a call to
> phy_init_hw(), which takes the PHY out of SPD and performs full
> reinitialization.
> 
> Fixes: f25a7eaa897f ("net: phy: micrel: Add ksz9131_resume()")
> Signed-off-by: Ovidiu Panait <[email-masked]>
> ---
>  drivers/net/phy/micrel.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/phy/micrel.c b/drivers/net/phy/micrel.c
> index 2aa1dedd21b8..4236dbf4ad6b 100644
> --- a/drivers/net/phy/micrel.c
> +++ b/drivers/net/phy/micrel.c
> @@ -6016,8 +6016,13 @@ static int lan8841_suspend(struct phy_device 
> *phydev)
> 
>  static int ksz9131_resume(struct phy_device *phydev)
>  {
> -	if (phydev->suspended && phy_interface_is_rgmii(phydev))
> -		ksz9131_config_rgmii_delay(phydev);
> +	int ret;
> +
> +	if (phydev->suspended) {
> +		ret = phy_init_hw(phydev);
> +		if (ret)
> +			return ret;
> +	}

Fix looks correct.

nit: phy_init_hw() already clears PDOWN, so the PDOWN clear and
1ms sleep in kszphy_resume() become redundant. But this is probably
something for a future cleanup.

> 
>  	return kszphy_resume(phydev);
>  }

Reviewed-by: Nicolai Buchwitz <[email-masked]>